Semiconductor laser, electronic apparatus, and method of driving semiconductor laser

ABSTRACT

In a semiconductor laser according to an embodiment of the present disclosure, a ridge part has a structure in which a plurality of gain regions and a plurality of Q-switch regions are each disposed alternately with each of separation regions being interposed therebetween in an extending direction of the ridge part. The separation regions each have a separation groove that separates from each other, by a space, the gain region and the Q-switch region adjacent to each other. The separation groove has a bottom surface at a position, in a second semiconductor layer, higher than a part corresponding to a foot of each of both sides of the ridge part. The semiconductor laser includes an electrode provided over the bottom surface of each separation groove with an insulating layer being interposed therebetween.

TECHNICAL FIELD

The present disclosure relates to a semiconductor laser, an electronicapparatus, and a method of driving the semiconductor laser.

BACKGROUND ART

In a semiconductor laser, there is a Q-switch operation as a method ofobtaining a high-power pulse by controlling oscillation. In the Q-switchoperation, optical loss is initially increased to suppress oscillation,thereby facilitating optical pumping to cause the number of atoms inexcited states to sufficiently increase; at that point in time, aQ-value is raised, thus allowing for oscillation. The semiconductorlaser that allows for the Q-switch operation is described in thefollowing PTLs 1 to 5, for example.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. H1-262683

PTL 2: Japanese Unexamined Patent Application Publication No. H5-90700

PTL 3: Japanese Unexamined Patent Application Publication No. H10-229252

PTL 4: Japanese Unexamined Patent Application Publication No. 2005-39099

PTL 5: Japanese Unexamined Patent Application Publication No.2008-258274

SUMMARY OF THE INVENTION

In a semiconductor laser that allows for a Q-switch operation, a currentleakage may occur in some cases between a gain region and a Q-switchregion. The current leakage that occurs between the gain region and theQ-switch region causes an adverse effect on the Q-switch operation. Itis therefore desirable to provide a semiconductor laser, an electronicapparatus, and a method of driving the semiconductor laser that make itpossible to suppress a current leakage.

A semiconductor laser according to an embodiment of the presentdisclosure includes, on a semiconductor substrate, a first semiconductorlayer of a first conductivity type, an active layer, and a secondsemiconductor layer of a second conductivity type, in this order. Thesemiconductor laser further includes a ridge part formed in the secondsemiconductor layer and extending in a stacked in-plane direction. Theridge part has a structure in which a plurality of gain regions and aplurality of Q-switch regions are each disposed alternately with each ofseparation regions being interposed therebetween in an extendingdirection of the ridge part. The separation regions each have aseparation groove that separates from each other, by a space, the gainregion and the Q-switch region adjacent to each other. The separationgroove has a bottom surface at a position, in the second semiconductorlayer, higher than a part corresponding to a foot of each of both sidesof the ridge part. The semiconductor laser further includes an electrodeprovided over the bottom surface of each separation groove with aninsulating layer being interposed therebetween.

An electronic apparatus according to an embodiment of the presentdisclosure includes the semiconductor laser as a light source.

A method of driving a semiconductor laser according to an embodiment ofthe present disclosure is a method of driving the semiconductor laserincluding: applying a forward bias pulse voltage to a gain region;applying a reverse bias to a Q-switch region; and applying a forwardbias to an electrode.

In the semiconductor laser, the electronic apparatus, the method ofdriving the semiconductor laser according to the respective embodimentsof the present disclosure, the bottom surface of the separation groovein the ridge part is provided at a position, in the second semiconductorlayer of the second conductivity type, higher than the partcorresponding to the foot of each of both the sides of the ridge part.Further, the electrode is provided over the bottom surface of theseparation groove provided in the ridge part with the insulating layerbeing interposed therebetween. Accordingly, a depletion region formedbetween the gain region and the Q-switch region causes a part betweenthe gain region and the Q-switch region to have a higher resistance.Moreover, light scattering of carriers in the gain region is suppressedto increase injection carrier density.

According to the semiconductor laser, the electronic apparatus, themethod of driving the semiconductor laser of the respective embodimentsof the present disclosure, the depletion region formed between the gainregion and the Q-switch region causes the part between the gain regionand the Q-switch region to have a higher resistance, and the lightscattering of carriers in the gain region is suppressed to increase theinjection carrier density. Thus, it becomes possible to suppress acurrent leakage. It is to be noted that the effects of the presentdisclosure are not necessarily limited to those described here, and maybe any of the effects described in the present specification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a configuration example of a top surface of asemiconductor laser according to a first embodiment of the presentdisclosure.

FIG. 2 illustrates a perspective configuration example of thesemiconductor laser illustrated in FIG. 1.

FIG. 3 illustrates a perspective configuration example of a portion ofthe semiconductor laser illustrated in FIG. 2 excluding bank parts.

FIG. 4 illustrates a cross-sectional configuration example of thesemiconductor laser illustrated in FIG. 1 taken along a line A-A.

FIG. 5 illustrates a cross-sectional configuration example of thesemiconductor laser illustrated in FIG. 1 taken along a line B-B.

FIG. 6 illustrates a cross-sectional configuration example of thesemiconductor laser illustrated in FIG. 1 taken along a line C-C.

FIG. 7 illustrates a cross-sectional configuration example of thesemiconductor laser illustrated in FIG. 1 taken along a line D-D.

FIG. 8 illustrates a perspective configuration example of asemiconductor laser device mounted with the semiconductor laserillustrated in FIG. 1 on a sub-mount.

FIG. 9 illustrates a cross-sectional configuration example of a wafer ina manufacturing process of the semiconductor laser illustrated in FIG.1.

FIG. 10 illustrates a cross-sectional configuration example of the waferin a manufacturing process subsequent to FIG. 9.

FIG. 11 illustrates a cross-sectional configuration example of the waferin a manufacturing process subsequent to FIG. 10.

FIG. 12A illustrates a cross-sectional configuration example of thewafer in a manufacturing process subsequent to FIG. 11.

FIG. 12B illustrates a cross-sectional configuration example of thewafer in a manufacturing process subsequent to FIG. 11.

FIG. 12C illustrates a cross-sectional configuration example of thewafer in a manufacturing process subsequent to FIG. 11.

FIG. 13 illustrates a cross-sectional configuration example of the waferin a manufacturing process subsequent to FIG. 12A.

FIG. 14A illustrates an example of a depletion region generated in thesemiconductor laser illustrated in FIG. 1.

FIG. 14B illustrates an example of a depletion region generated in thesemiconductor laser illustrated in FIG. 1.

FIG. 15 illustrates an example of waveforms of voltages to be applied tothe semiconductor laser illustrated in FIG. 1.

FIG. 16 illustrates an example of waveforms of voltages to be applied tothe semiconductor laser illustrated in FIG. 1.

FIG. 17 illustrates an example of changes in optical outputs over time.

FIG. 18 illustrates an example of a change in a carrier density of eachgain region over time.

FIG. 19 illustrates an example of a change in a carrier density of eachgain region over time.

FIG. 20 illustrates an example of a change in a carrier density of eachgain region over time.

FIG. 21 illustrates an example of waveforms of voltages to be applied tothe semiconductor laser illustrated in FIG. 1.

FIG. 22 illustrates a modification example of the perspectiveconfiguration of the semiconductor laser illustrated in FIG. 1.

FIG. 23 illustrates a modification example of the cross-sectionalconfiguration of the semiconductor laser illustrated in FIG. 1 takenalong the line B-B.

FIG. 24 illustrates a modification example of the cross-sectionalconfiguration of the semiconductor laser illustrated in FIG. 1 takenalong the line A-A.

FIG. 25 illustrates a modification example of the cross-sectionalconfiguration of the semiconductor laser illustrated in FIG. 1 takenalong the line A-A.

FIG. 26 illustrates a modification example of the cross-sectionalconfiguration of the semiconductor laser illustrated in FIG. 1 takenalong the line B-B.

FIG. 27 illustrates a modification example of the cross-sectionalconfiguration of the semiconductor laser illustrated in FIG. 1 takenalong the line A-A.

FIG. 28 illustrates a schematic configuration example of a distancemeasuring unit according to a second embodiment of the presentdisclosure.

FIG. 29 illustrates a modification example of the schematicconfiguration of the distance measuring unit illustrated in FIG. 28.

FIG. 30 illustrates a modification example of the schematicconfiguration of the distance measuring unit illustrated in FIG. 28.

FIG. 31 illustrates a modification example of the schematicconfiguration of the distance measuring unit illustrated in FIG. 28.

MODES FOR CARRYING OUT THE INVENTION

In the following, embodiments for carrying out the present disclosureare described in detail with reference to drawings. The followingdescription is directed to specific examples of the present disclosure,and the present disclosure is not limited to the following embodiments.Moreover, the present disclosure is not limited to positions,dimensions, dimension ratios, and other factors of respective componentsillustrated in the drawings. It is to be noted that the description isgiven in the following order.

1. First Embodiment (Semiconductor Laser)

An example in which only a gain region is provided with an impuritydiffusion region

2. Modification Examples of First Embodiment (Semiconductor Laser)

An example in which there is no protrusion of a separation region in awidth-direction

An example in which an impurity diffusion region is formed only in aridge part

An example in which a Q-switch region is also provided with an impuritydiffusion region

3. Second Embodiment (Distance Measuring Unit)

An example in which a semiconductor laser according to any of theforegoing embodiment and modification examples thereof is used as alight source of a distance measuring unit

1. First Embodiment [Configuration]

Description is given of a configuration of a semiconductor laser 1according to a first embodiment of the present disclosure. FIG. 1illustrates a configuration example of a top surface of thesemiconductor laser 1 according to the present embodiment. FIG. 2illustrates a perspective configuration example of the semiconductorlaser 1 illustrated in FIG. 1. FIG. 3 illustrates a perspectiveconfiguration example of a portion of the semiconductor laser 1illustrated in FIG. 1 excluding bank parts 20C (described later).

The semiconductor laser 1 is an element that generates an optical pulse,and is used suitably, for example, as a light source of a laser radar, alaser for processing, a medical laser scalpel, and the like. Thesemiconductor laser 1 is an edge-emitting laser. The semiconductor laser1 includes a front end surface S1 and a rear end surface S2 that areopposed to each other in a resonator-direction, and a raised ridge part20A interposed between the front end surface S1 and the rear end surfaceS2. The semiconductor laser 1 has a length of 1,000 μm, for example, inthe resonator-direction. The length of the semiconductor laser 1 in theresonator-direction is appropriately adjustable depending on necessarycharacteristics. The ridge part 20A extends in the resonator-direction.One end surface of the ridge part 20A is exposed to the front endsurface S1, for example, and the other end surface of the ridge part 20Ais exposed to the rear end surface S2, for example. It is to be notedthat the respective end surfaces of the ridge part 20A may be providedat positions recessed slightly from the front end surface S1 and therear end surface S2. In this case, it follows that the respective endsurfaces of the ridge part 20A are not provided in the same plane as thefront end surface S1 and the rear end surface S2. At this occasion, acurrent non-injection region 20 d described later may not be necessarilyprovided.

The front end surface S1 and the rear end surface S2 are each a surfaceformed by cleavage. The front end surface S1 and the rear end surface S2each serve as a resonator mirror, and the ridge part 20A serves as anoptical waveguide. The front end surface S1 is provided with ananti-reflection film, for example. The anti-reflection film includes,for example, a dielectric (e.g., SiO₂, TiO₂, Ta₂O₅, SiN, etc.), and isconfigured to have a reflectance of about 15% at the front end surfaceS1. The rear end surface S2 is provided with a multilayer reflectionfilm, for example. The multilayer reflection film includes, for example,a dielectric (e.g., SiO₂, TiO₂, Ta₂O₅, SiN, etc.) and Si, and isconfigured to have a reflectance of about 85% at the rear end surfaceS2.

The semiconductor laser 1 includes the bank parts 20C in a raised shapeat respective sides of the ridge part 20A. In other words, thesemiconductor laser 1 has a double-ridge structure configured by theridge part 20A and the two bank parts 20C. The bank parts 20C are eachprovided for the purpose of protecting the ridge part 20A and ofsecuring a region for wire-bonding. The bank parts 20C each extend, forexample, in a direction parallel to the extending direction of the ridgepart 20A. Each of the bank parts 20C may be omitted as necessary. Thesemiconductor laser 1 is a multi-electrode semiconductor laser providedwith a multiplicity of electrodes on the ridge part 20A.

The ridge part 20A is configured by a plurality of gain regions 20 a, aplurality of Q-switch regions 20 b, and a plurality of separationregions 20 c, for example. The plurality of gain regions 20 a and theplurality of Q-switch regions 20 b are each disposed alternately withthe separation region 20 c being interposed therebetween in theextending direction of the ridge part 20A. In other words, the ridgepart 20A has a structure in which the plurality of gain regions 20 a andthe plurality of Q-switch regions 20 b are each disposed alternatelywith the separation region 20 c being interposed therebetween in theextending direction of the ridge part 20A. Each of the separationregions 20 c is disposed between the gain region 20 a and the Q-switchregion 20 b. Each of the separation regions 20 c is configured by aseparation groove 20B in a recessed shape provided in the ridge part 20Aand by a part, of the ridge part 20A, immediately below the separationgroove 20B. It is preferable that the gain regions 20 a each have alength of 500 μm or less, desirably 300 μm or less. When the gainregions 20 a each have a length more than 500 μm, carrier density isless likely to be increased, and thus it becomes highly possible that anoptical output may be lowered. Meanwhile, when the gain regions 20 aeach have a length of 300 μm or less, particularly the carrier densityis more likely to be increased, thus making it easier to enhance theoptical output.

Either the Q-switch region 20 b or the gain region 20 a may be providedat an end of the ridge part 20A on side of the front end surface S1.Further, either the Q-switch region 20 b or the gain region 20 a may beprovided at an end of the ridge part 20A on side of the rear end surfaceS2. Moreover, the current non-injection region 20 d may be provided atboth the ends of the ridge part 20A. The current non-injection region 20d is a region that suppresses unstable oscillation caused by a currentflowing in a vicinity of the front end surface S1 or the rear endsurface S2. The current non-injection region 20 d is a region where nocontact layer 27 described later is provided, and is a region where nocurrent is injected directly from an electrode.

FIG. 4 illustrates a cross-sectional configuration example of thesemiconductor laser 1 illustrated in FIG. 1 taken along a line A-A. FIG.5 illustrates a cross-sectional configuration example of thesemiconductor laser 1 illustrated in FIG. 1 taken along a line B-B. FIG.6 illustrates a cross-sectional configuration example of thesemiconductor laser 1 illustrated in FIG. 1 taken along a line C-C. FIG.7 illustrates a cross-sectional configuration example of thesemiconductor laser 1 illustrated in FIG. 1 taken along a line D-D. FIG.8 illustrates a perspective configuration example of a semiconductorlaser device 2 mounted with the semiconductor laser 1 illustrated inFIG. 1 on a sub-mount 201 (described later).

The semiconductor laser 1 includes a substrate 10 and a semiconductorlayer 20 formed on the substrate 10. The semiconductor layer 20includes, for example, a lower cladding layer 21, a lower guide layer22, an active layer 23, an upper guide layer 24, a first upper claddinglayer 25, a second upper cladding layer 26, and a contact layer 27 inthis order, from side of the substrate 10. The semiconductor layer 20may include a layer other than those described above. The semiconductorlayer 20 may include a buffer layer at a position between the lowercladding layer 21 and the substrate 10, for example.

The substrate 10 is, for example, a Si-doped n-type GaAs substrate. Thelower cladding layer 21 includes, for example, Si-doped n-typeAl_(x1)Ga_(1-x1)As (0.2<x1<0.5). The lower guide layer 22 includes, forexample, Si-doped n-type Al_(x2)Ga_(1-x2)As (0.1<x1<0.3). The bufferlayer includes, for example, Si-doped n-type Al_(0.3)Ga_(0.7)As. Aconcentration of Si included in the substrate 10, the lower claddinglayer 21, the lower guide layer 22, and the buffer is about 5×10¹⁷ cm⁻³,for example.

The active layer 23 has a multiple quantum well structure, for example.The multiple quantum well structure is, for example, a structure inwhich a barrier layer and a well layer are stacked alternately. Thebarrier layer includes, for example, Al_(0.3)Ga_(0.9)As. The well layerincludes, for example, Al_(0.4)Ga_(0.6)As. In the active layer 23, adopant and a doping concentration in the multiple quantum well structurethat configures the active layer 23 are adjusted to allow an averageelectric property of the active layer 23 to be of p-type.

The upper guide layer 24 includes, for example, C-doped p-typeAl_(0.3)Ga_(0.7)As. The first upper cladding layer 25 includes, forexample, C-doped p-type Al_(0.5)Ga_(0.5)As. The first upper claddinglayer 25 includes, for example, etching stop layers 25A and 25B that aredisposed apart from each other. The etching stop layers 25A and 25B areeach a semiconductor layer having a composition ratio different from acomposition ratio of another part of the first upper cladding layer 25.The etching stop layer 25A is disposed closer to the substrate 10 thanthe etching stop layer 25B to the substrate 10, and includes, forexample, C-doped p-type Al_(0.3)Ga_(0.7)As. The etching stop layer 25Bis disposed more distant from the substrate 10 than the etching stoplayer 25A from the substrate 10, and includes, for example, C-dopedp-type Al_(0.3)Ga_(0.7)As. A layer, of the first upper cladding layer25, interposed between the etching stop layer 25A and the etching stoplayer 25B has a thickness t2 that is a thickness equal to t1±50 nm, forexample, provided that t1 denotes a thickness of the contact layer 27.The thickness t2 is a thickness equal to or more than 100 nm, forexample.

The second upper cladding layer 26 includes, for example, C-doped p-typeAl_(0.5)Ga_(0.5)As. The contact layer 27 includes, for example, C-dopedp-type GaAs. The active layer 23, the upper guide layer 24, the firstupper cladding layer 25, the second upper cladding layer 26, and thecontact layer 27 each have a conductivity type that is different from aconductivity type of each of the substrate 10, the buffer layer, thelower cladding layer 21, and the lower guide layer 22. Specifically, theactive layer 23, the upper guide layer 24, the first upper claddinglayer 25, the second upper cladding layer 26, and the contact layer 27each have p-conductivity type, whereas the substrate 10, the bufferlayer, the lower cladding layer 21, and the lower guide layer 22 eachhave n-conductivity type. Accordingly, an interface between the lowerguide layer 22 and the active layer 23 serves as a p-n junction 20J.That is, the semiconductor layer 20 includes the p-n junction 20J at aposition lower than a part corresponding to a foot of each of both sidesof the ridge part 20A.

The semiconductor laser 1 includes an impurity diffusion region 25C at alocation, of the first upper cladding layer 25, corresponding to thegain region 20 a and regions at both sides thereof. The impuritydiffusion region 25C is in contact with the second upper cladding layer26 in the gain region 20 a. The impurity diffusion region 25C has thesame conductivity type as that of each of the first upper cladding layer25 and the second upper cladding layer 26. The impurity diffusion region25C is, for example, a region formed by diffusing Zn to the first uppercladding layer 25. Accordingly, at a location, of the first uppercladding layer 25, corresponding to the gain region 20 a, thesemiconductor laser 1 has a region (the impurity diffusion region 25C)having a relatively higher p-type impurity concentration than a location(the Q-switch region 20 b), of the first upper cladding layer 25,different from the location corresponding to the gain region 20 a. Alower end of the impurity diffusion region 25C either may be positionedat an interface between the first upper cladding layer 25 and the upperguide layer 24, or may be positioned in the first upper cladding layer25, in the upper guide layer 24, or in the active layer 23. The impuritydiffusion region 25C has a Zn diffusion concentration of about 1×10¹⁷cm⁻³ to about 1×10¹⁹ cm⁻³. It is to be noted that the second uppercladding layer 26 preferably has a C concentration that is lower thanthe Zn diffusion concentration of the impurity diffusion region 25C. Insuch a case, optical absorption performed by C becomes smaller, thusenhancing the optical output.

The contact layer 27 is exposed to a top surface of the gain region 20a. The etching stop layer 25A is exposed to both sides of the gainregion 20 a (both sides of a part, of the ridge part 20A, correspondingto the gain region 20 a). The gain region 20 a has a heightcorresponding to a thickness from a top surface of the etching stoplayer 25A to a top surface of the contact layer 27. Each of both thesides of the gain region 20 a (both the sides of the part, of the ridgepart 20A, corresponding to the gain region 20 a) is dug from the contactlayer 27 to a location corresponding to the top surface of the etchingstop layer 25A. The gain region 20 a is configured by the impuritydiffusion region 25C, the second upper cladding layer 26, and thecontact layer 27, and serves as a p-type semiconductor region.

The contact layer 27 is exposed to a top surface of the Q-switch region20 b. The etching stop layer 25A is exposed to both sides of theQ-switch region 20 b (both sides of a part, of the ridge part 20A,corresponding to the Q-switch region 20 b). The Q-switch region 20 b hasa height corresponding to a thickness from the top surface of theetching stop layer 25A to the top surface of the contact layer 27. Eachof both the sides of the Q-switch region 20 b (both the sides of thepart, of the ridge part 20A, corresponding to the Q-switch region 20 b)is dug from the contact layer 27 to the top surface of the etching stoplayer 25A. The Q-switch region 20 b is configured by the first uppercladding layer 25, the second upper cladding layer 26, and the contactlayer 27, and serves as the p-type semiconductor region.

The etching stop layer 25B is exposed to a top surface of the separationregion 20 c. A part, of the etching stop layer 25B, exposed to the topsurface of the separation region 20 c is a surface formed by wetetching, for example, and is cleaned with dilute hydrochloric acid,etc., for example. The etching stop layer 25A is exposed to both sidesof the separation region 20 c (both sides of a part, of the ridge part20A, corresponding to the separation region 20 c). A surface of a part,of the etching stop layer 25A, corresponding to the foot of each of boththe sides of the ridge part 20A is a surface formed by wet etching, forexample, and is cleaned with dilute hydrochloric acid, etc., forexample. The separation region 20 c has a height corresponding to athickness from the top surface of the etching stop layer 25A to the topsurface of the etching stop layer 25B. Each of both the sides of theseparation region 20 c (both the sides of the part, of the ridge part20A, corresponding to the separation region 20 c) is dug from thecontact layer 27 to a location corresponding to the top surface of theetching stop layer 25A. The separation groove 20B separates the adjacentgain region 20 a and Q-switch region 20 b from each other by a space. Abottom surface of the separation groove 20B is provided in the firstupper cladding layer 25. Specifically, the bottom surface of theseparation groove 20B corresponds to the top surface of the etching stoplayer 25B, and is provided at a position higher than the part (theetching stop layer 25A) corresponding to the foot of each of both thesides of the ridge part 20A. The separation region 20 c has a width (awidth of the ridge part 20A in a width-direction) D3 that is larger thana width D1 of the gain region 20 a as well as a width D2 of the Q-switchregion 20 b. This makes it possible to suppress scattering of guidedlight caused by the separation groove 20B. A part, of the separationregion 20 c, corresponding to a bottom of the separation groove 20B isconfigured by the first upper cladding layer 25 (including the etchingstop layers 25A and 25B), and serves as the p-type semiconductor region.

The second upper cladding layer 26 is exposed to a top surface of thecurrent non-injection region 20 d. The etching stop layer 25A is exposedto both sides of the current non-injection region 20 d (both sides of apart, of the ridge part 20A, corresponding to the current non-injectionregion 20 d). The current non-injection region 20 d has a heightcorresponding to a thickness from the top surface of the etching stoplayer 25A to a top surface of the second upper cladding layer 26. Eachof both the sides of the current non-injection region 20 d (both thesides of the part, of the ridge part 20A, corresponding to the currentnon-injection region 20 d) is dug from the contact layer 27 to alocation corresponding to the top surface of the etching stop layer 25A.

The semiconductor laser 1 further includes, on the semiconductor layer20, for example, an insulating layer 28, a dielectric layer 29, a gainelectrode 31, a Q-switch electrode 32, a separation electrode 33, andpad electrodes 34, 35, and 36. The insulating layer 28 is a layer thatprotects the semiconductor layer 20, and covers an entire top surface ofthe semiconductor layer 20. The insulating layer 28 is configured, forexample, by an insulating inorganic material such as SiO₂. Thedielectric layer 29 is a layer that reduces capacitance of each of thepad electrodes 33 and 34. The dielectric layer 29 is provided in contactwith a part, of a surface of the insulating layer 28, immediately abovethe bank part 20C, and is configured, for example, by SiO₂, polyimide,or the like.

The insulating layer 28 has a plurality of openings on respective partsimmediately above the ridge part 20A. The plurality of openings providedin the insulating layer 28 are assigned on a one-to-one basis torespective gain regions 20 a and respective Q-switch regions 20 b. Thegain electrode 31 is formed in the opening formed at a part, of theinsulating layer 28, immediately above the gain region 20 a. The gainelectrode 31 is formed in contact with the top surface of the ridge part20A (the top surface of the contact layer 27). The gain electrode 31 isan electrode that injects a current into the gain region 20 a, and isconfigured by a metal material. The Q-switch electrode 32 is formed inthe opening formed at a part, of the insulating layer 28, immediatelyabove the Q-switch region 20 b. The Q-switch electrode 32 is formed incontact with the top surface of the ridge part 20A (the top surface ofthe contact layer 27). The Q-switch electrode 32 is an electrode thatapplies a bias voltage to the Q-switch region 20 b, and is configured bya metal material. The separation electrode 33 is formed over the bottomsurface of the separation groove 20B, with the insulating layer 28 beinginterposed therebetween. The separation electrode 33 is formed incontact with a surface, of the insulating layer 28, in the separationregion 20 c. The separation electrode 33 is an electrode for formationof a depletion region 37 (described later) in the separation region 20c, and is configured by a metal material.

The pad electrodes 34, 35, and 36 are each formed on the bank part 20C,and is specifically formed on the dielectric layer 29. The pad electrode34 is an electrode for bonding of a wire 203, and is electricallycoupled to the gain electrode 31. The pad electrode 35 is an electrodefor bonding of a wire 204, and is electrically coupled to the Q-switchelectrode 32. The pad electrode 36 is an electrode for bonding of a wire205, and is electrically coupled to the separation electrode 33. The padelectrodes 34, 35, and 36 are each configured by a metal material.

The semiconductor laser 1 further includes, for example, a lowerelectrode 40 in contact with a back surface of the substrate 10. Thelower electrode 40, as well as the gain electrode 31 and the Q-switchelectrode 32, is an electrode for driving of the semiconductor laser 1.The lower electrode 40 is configured by a metal material. In a casewhere the semiconductor laser 1 is mounted on the sub-mount 201, thelower electrode 40 is coupled to a sheet-shaped electrode 202 on thesub-mount 201 via, for example, a solder such as AuSn. The electrode 202is also an electrode for bonding of the wire 205. The sub-mount 201 isconfigured by an insulating material having a high heat dissipationproperty.

[Manufacturing Method]

Next, description is given of a manufacturing method of thesemiconductor laser 1 according to the present embodiment. FIG. 9illustrates a cross-sectional configuration example of a wafer in amanufacturing process of the semiconductor laser 1. FIG. 10 illustratesa cross-sectional configuration example of the wafer in a manufacturingprocess subsequent to FIG. 9. FIG. 11 illustrates a cross-sectionalconfiguration example of the wafer in a manufacturing process subsequentto FIG. 10. FIGS. 12A, 12B, and 12C each illustrate a cross-sectionalconfiguration example of the wafer in a manufacturing process subsequentto FIG. 11. FIG. 12A illustrates a cross-sectional configuration exampleof a location corresponding to the line B-B illustrated in FIG. 1. FIG.12B illustrates a cross-sectional configuration example of a locationcorresponding to the line C-C illustrated in FIG. 1. FIG. 12Cillustrates a cross-sectional configuration example of a locationcorresponding to the line D-D illustrated in FIG. 1. FIG. 13 illustratesa cross-sectional configuration example of the wafer in a manufacturingprocess subsequent to FIG. 12A.

In order to manufacture the semiconductor laser 1, for example, acompound semiconductor is formed at once on the substrate 10 includingSi-doped n-type GaAs, by means of, for example, an epitaxial crystalgrowth method such as a metal organic chemical vapor deposition (MOCVD)method. Examples of a material to be used at this occasion for thecompound semiconductor include a methyl-based organic metal gas such astrimethylaluminum (TMAI), trimethylgallium (TMGa), trimethylindium(TMIn), and arsine (AsH₃)

First, the substrate 10 (wafer) is placed in an MOCVD furnace. Next, thelower cladding layer 21 (e.g., Si-doped n-type Al_(x1)Ga_(1-x1)As) andthe lower guide layer 22 (e.g., Si-doped n-type Al_(x2)Ga_(1-x2)As) areformed in this order on the substrate 10 (see FIG. 9). Subsequently, theactive layer 23 (e.g., a multiple quantum well structure in whichAl_(0.1)Ga_(0.9)As and Al_(0.4)Ga_(0.6)As are stacked alternately) isformed on the lower guide layer 22 (see FIG. 9). Next, the upper guidelayer 24 (e.g., p-type Al_(0.3)Ga_(0.7)As) and the first upper claddinglayer 25 (e.g., p-type Al_(0.5)Ga_(0.5)As) are formed in this order onthe active layer 23 (see FIG. 9). At this occasion, in the first uppercladding layer 25, the etching stop layer 25A (e.g., p-typeAl_(0.3)Ga_(0.7)As) and the etching stop layer 25B (e.g., p-typeAl_(0.3)Ga_(0.7)As) are formed apart from each other on the upper guidelayer 24 (see FIG. 9).

Next, the substrate 10 (wafer) is taken out of the MOCVD furnace. Next,Zn is diffused to a predetermined region of a surface of the first uppercladding layer 25. This allows the impurity diffusion region 25C to beformed (see FIG. 9). At this occasion, Zn is diffused not only to a partto be the ridge part 20A, but also to parts corresponding to both thesides of the ridge part 20A. This makes it possible to easily uniformizea Zn concentration of the part to be the ridge part 20A. A solid phasediffusion method using a ZnO film or a vapor phase diffusion method maybe used for diffusion of Zn. For example, the ZnO film is formed in thepredetermined region of the surface of the first upper cladding layer 25to perform solid phase diffusion. Thereafter, the ZnO film is detachedto cover the entire surface of the first upper cladding layer 25 withSiN, etc. Thereafter, the substrate 10 (wafer) is annealed, therebydiffusing Zn from a surface layer to a deep part of the first uppercladding layer 25, thus making it possible to decrease the Znconcentration of the surface layer to a desired concentration.

Next, the surface of the first upper cladding layer 25 is cleaned withdilute hydrochloric acid, etc., and thereafter the substrate 10 (wafer)is placed again in the MOCVD furnace. Next, the second upper claddinglayer 26 (e.g., C-doped p-type Al_(0.5)Ga_(0.5)As) and the contact layer27 (e.g., C-doped p-type GaAs) are formed in this order on the firstupper cladding layer 25. In this manner, the semiconductor layer 20 isformed on the substrate 10 (see FIG. 10).

Next, the substrate 10 (wafer) is taken out of the MOCVD furnace. Next,a CVD method, etc., for example, is used to form a hard mask (a filmincluding SiO₂, etc.) in a predetermined pattern on the surface of thesemiconductor layer 20 (the contact layer 27). Next, a dry etchingmethod, for example, is used to selectively etch the semiconductor layer20 via an opening formed in the hard mask, thereby, for example, diggingthe semiconductor layer 20 to a location immediately before reaching theetching stop layer 25B. Thereafter, for example, a wet etching methodemploying hydrofluoric acid is used to selectively etch thesemiconductor layer 20 via the opening formed in the hard mask, thereby,for example, digging the semiconductor layer 20 to the etching stoplayer 25B. In this manner, the separation groove 20B is formed (see FIG.11). Thereafter, the above-described hard mask is removed.

Next, a CVD method, for example, is used to newly form a hard mask (afilm including SiO₂, etc.) in a predetermined pattern. Next, a dryetching method, for example, is used to selectively etch thesemiconductor layer 20 via an opening formed in the hard mask, therebydigging a location corresponding to each of both the sides of the ridgepart 20A to a location immediately before reaching the etching stoplayer 25A. Thereafter, for example, a wet etching method employinghydrofluoric acid is used to selectively etch the semiconductor layer 20via the opening formed in the hard mask, thereby, for example, diggingthe semiconductor layer 20 to the etching stop layer 25A. In thismanner, the ridge part 20A and the two bank parts 20C are formed (seeFIGS. 12A, 12B, and 12C). Thereafter, the above-described hard mask isremoved.

It is to be noted that only the dry etching may be used to form theseparation groove 20B, the ridge part 20A, and the two bank parts 20C,without using the wet etching. In the case of the dry etching, it ispossible to highly accurately grasp an etching depth on a real-timebasis by monitoring optical interference. For example, upon reaching theetching stop layer 25B or the etching stop layer 25A, optical intensityvaries in accordance with the optical interference, thus making itpossible to recognize having reached a surface of the etching stop layer25B or the etching stop layer 25A by capturing the variance in theoptical intensity.

Next, for example, the CVD method, etc. is used to form the insulatinglayer 28 on an entire surface of each of components including theseparation groove 20B, the ridge part 20A, and the two bank parts 20C(see FIG. 13). Next, for example, the CVD method, etc. is used to formthe dielectric layer 29 on the insulating layer 28, immediately abovethe bank part 20C. Next, for example, a vapor deposition method, etc. isused to form the gain electrode 31 in the opening, of the insulatinglayer 28, formed immediately above each of the gain regions 20 a, and toform the Q-switch electrode 32 in the opening, of the insulating layer28, formed immediately above each of the Q-switch regions 20 b (see FIG.13). Further, for example, the vapor deposition method is used to formthe separation electrode 33 on the surface, of the insulating layer 28,in the separation region 20 c, (see FIG. 13). Next, for example, thevapor deposition method, etc. is used to form each of the pad electrodes34, 35, and 36 on the insulating layer 28 and the dielectric layer 29.At this occasion, in order to prevent a short circuit between the padelectrode 35 and the pad electrode 36, an insulating layer 28A (see FIG.7) including SiO₂, etc. is formed in advance, before formation of thepad electrode 36, on a surface, of the pad electrode 35, where the padelectrode 36 is to be formed. Moreover, as necessary, the pad electrodes34, 35, and 36 are each made thicker as a film using a plating method,for example. By making each of the pad electrodes 34, 35, and 36 thickeras a film, it becomes possible to prevent each of the pad electrodes 34,35, and 36 from severing between the ridge part 20A and the bank part20C.

Next, as necessary, the back surface of the substrate 10 is ground toadjust a thickness of the substrate 10 to a desired thickness. Next, forexample, the vapor deposition method, etc. is used to form the lowerelectrode 40 on the back surface of the substrate 10. Next, thesubstrate 10 (wafer) is subjected to cleavage to form the front endsurface S1 and the rear end surface S2. Lastly, the anti-reflection filmis formed on the front end surface S1, and the multilayer reflectionfilm is formed on the rear end surface S2. In this manner, thesemiconductor laser 1 is manufactured.

In the semiconductor laser 1 thus manufactured, a drive circuit (e.g., alaser driver 304 described later) outputs, for example, a forward bias(a pulse voltage V1) having an amplitude of several volts and a pulsewidth of a nano-second (ns) order (e.g., about 1 ns). Accordingly, forexample, a voltage of the gain region 20 a (the gain electrode 31)becomes equivalent to the pulse voltage V1, as illustrated in FIGS. 15and 16. Further, the drive circuit (e.g., the laser driver 304 describedlater) outputs, for example, a reverse bias (a voltage V2) of negativeseveral volts (voltage V2<0). Accordingly, for example, a voltage of theQ-switch region 20 b (the Q-switch electrode 32) becomes equivalent tothe voltage V2, as illustrated in FIGS. 15 and 16. Further, the drivecircuit (e.g., the laser driver 304 described later) outputs, forexample, a forward bias (a voltage V3) of positive several volts(voltage V3>pulse voltage V1). Accordingly, for example, a voltage ofthe separation region 20 c becomes equivalent to the voltage V3, asillustrated in FIGS. 15 and 16.

At this occasion, for example, the voltage V2 either may be a directcurrent (DC) (fixed value) as illustrated in FIG. 15, or may be a pulsevoltage according to application of the pulse voltage V1 as illustratedin FIG. 16. The voltage V2 may be, for example, a pulse voltage thatbecomes larger in a negative direction during a period including aperiod from a rising time to a peak time of the pulse voltage V1. Thevoltage V3 is, for example, a direct current (DC) (fixed value) asillustrated in FIGS. 15 and 16. At this occasion, in the gain region 20a, carriers are gradually accumulated in the active layer 23, as acurrent flowing into the gain region 20 a becomes larger in associationwith the application of the pulse voltage V1. At a point in time whenthe carrier density exceeds an oscillation threshold, a photon densityincreases rapidly to cause laser oscillation to occur. This causesaccumulated electron-hole pairs to be rapidly consumed, and, from apoint in time when the carrier density falls below an oscillationthreshold density, the photon density rapidly decreases to stop thelaser oscillation. This allows for obtainment of a laser light pulse ofa pulse width (a pulse width of 200 ps or less, for example) shorterthan a pulse width of the pulse voltage V1 itself, as indicated by athick line in FIG. 17.

It is to be noted that a broken line in FIG. 17 indicates an example ofa laser light pulse in a case where the Q-switch region 20 b isgrounded. The laser light pulse indicated by the broken line in FIG. 17has a pulse width of about sub-ns. In a case where the Q-switch region20 b is grounded, there is less voltage drop caused by a photovoltaiccurrent generated in the Q-switch region 20 b; the Q-switch region 20 boperates as a absorbent having less voltage fluctuation, thus allowingfor obtainment of an optical pulse closer to a waveform of the pulsevoltage V1.

It has been known, for a behavior of the carrier density of the activelayer in the Q-switch operation, that a modeling is possible usingtraveling-wave rate equation (TRE) (Reference Literature: Ultrafastdiode lasers, Peter Vasilev, Atech House Publishers). FIGS. 18, 19, and20 each illustrate an example of results of verification of a model inaccordance with the semiconductor laser 1 performed uniquely by thepresent inventors with reference to a TRE method. FIG. 18 illustrates atransient response after provision of two gain regions 20 a at aresonator length of 1,000 μm and input of a step current of 4 A. FIG. 19illustrates a transient response after provision of five gain regions 20a at a resonator length of 1,000 μm and input of a step current of 4 A.FIG. 20 illustrates a transient response after provision of nine gainregions 20 a at a resonator length of 1,000 μm and input of a stepcurrent of 4 A. In all of FIGS. 18, 19, and 20, a reverse bias isapplied to the Q-switch region 20 b.

The carrier density of the gain region 20 a gradually increases to reacha peak value (1.2×10²⁵ cm⁻³) at about 0.6 ns. Meanwhile, at an end ofthe gain region 20 a, the carrier density is saturated at a degreeslightly larger than a transparent carrier density. One reason for thisis that light in each of the gain regions 20 a promotes stimulatedemission. In FIG. 19, a region where the carrier density is reduced dueto the stimulated emission is decreased. It is appreciated, in FIG. 20,that an average carrier density is increased. In this manner, in aQ-switch semiconductor laser in which high current injection isperformed into the gain region 20 a, it is preferable that the gainregions 20 a each have a length of 500 μm or less, desirably 300 μm orless. However, due to increase in the number of division of theresonator length, the number of the separation region is increased, thuslowering combined resistance of a part between the gain region 20 a andthe Q-switch region 20 b. The number of the division is preferablyadjusted to allow the combined resistance to be 100 kohms or more.

A carrier lifetime of the gain region 20 a depends on the square of thecarrier density. Accordingly, the carrier lifetime of the gain region 20a is saturated at the time of the high current injection. A typicalsemiconductor laser performs laser oscillation at a carrier densitysufficiently lower than a saturation carrier density. When a reversebias is adjusted to allow a loss of the Q-switch region 20 b to bebarely lower than a maximum gain in the saturation carrier density ofthe gain region 20 a, the laser oscillation occurs. In a case, forexample, where the reverse bias is applied through high resistance inaccordance with FIG. 15, voltage drop occurs due to a photocurrent ofthe Q-switch region 20 b, and thus the reverse bias becomes small tocause a Q-value of the semiconductor laser 1 to increase sharply. Thisallows for obtainment of pulse light having a high peak value. When acurrent leakage from the gain region 20 a to the Q-switch region 20 bbecomes larger, voltage drop occurs at a high resistance. Accordingly,there are several undesirable influences such as difficulty inapplication of the reverse bias to the Q-switch region 20 b, a loweredpeak value of the pulse light due to smaller fluctuation of the Q-value,or increase in the pulse width. As such a passive Q-switch method, thestructure of the semiconductor laser 1 according to the presentembodiment is applicable.

Meanwhile, as illustrated in FIGS. 18, 19, and 20, the carrier densityof the gain region 20 a reaches a peak value about 0.6 ns behind. Inaccordance with FIG. 16, the reverse voltage is applied to the Q-switchregion 20 b before application of a pulse current of the gain region 20a, and the loss of the Q-switch region 20 b is actively lowered afterthe saturation of the carrier density of the gain region 20 a; at thisoccasion, a gain exceeds the loss, thus causing the laser oscillation tooccur. The photocurrent of the Q-switch region 20 b undergoes voltagedrop similarly to the passive Q-switch method. Accordingly, anincreasing speed of the Q-value is enhanced, thus allowing forobtainment of the pulse light having a high peak value. A saturationtime of the carrier density is within about 3 ns, because it depends ona structure, etc. of the active layer 23. Accordingly, it is notdesirable that a width of the pulse current for the gain region 20 a be5 ns or more, because of increase in a reactive current.

[Effects]

Next, description is given of effects of the semiconductor laser 1according to the present embodiment.

There has been remarkable progress in recent 3D shape measurementtechniques, and such 3D shape measurement techniques have been activelyutilized in fields such as a gesture input in game devices and variouselectronics products as well as preventive safety and automatic drivingof automobiles. Laser radar using a time-of-flight (TOF) method is adirect method that allows for measurement of time until pulse lighthaving been applied to an object is scattered and returned as well asmeasurement of a distance to the object; the laser radar has been widelyused. The laser radar has limitations on a range of use, depending onperformance of devices that configure a system. The higher a pulseenergy of a laser light source becomes, the longer a distance to bemeasured becomes, allowing distance accuracy to be enhanced. There aremany industrial advantages of the semiconductor laser that is able todirectly generate pulse light, as follows: it is possible to provide thesemiconductor laser in a smaller size and less expensively; and it ispossible to achieve a high electricity-light conversion efficiency andlower power consumption. B. Lanz et al. obtains a pulse width of 80 psand a pulse energy of 3 nJ using a wide-stripe semiconductor laserhaving a saturable absorption property (Brigitte Lanz, Boris S. Ryvkin,Eugene A. Avrutin, and Juha T. Kostamovaara, “Performance improvement bya saturable absorber in gain-switched asymmetric-waveguide laserdiodes.” Opt. Express 29781, Vol. 21, 2013).

In order to increase a pulse energy using a semiconductor laser, it isnecessary to increase the number of carriers to be injected into a gainregion. Accordingly, several method are employed as follows: increasinga thickness of the active layer; increasing a width of a stripe; andapplying the reverse bias to a saturable absorption region to increasevariation in the Q-value. The method of varying the Q-value in theresonator in this manner is referred to as a Q-switch semiconductorlaser. A passive Q-switch semiconductor laser passively inducesvariation in the Q-value. An active Q-switch pulse semiconductor laseris able to modulate the reverse bias to be applied to the Q-switchregion to further increase the variation in the Q-value. In order tofurther increase the pulse energy, it is necessary to increase thevariation in the Q-value and to further increase a voltage to be appliedto the gain region. In particular, in a case where a watt-class pulsepeak value is obtained using a narrow stripe structure having a stripewidth of several μm or less, a potential difference between the Q-switchregion and the gain region becomes larger to reach 10 V or higher.

However, a typical Q-switch pulse semiconductor laser including AlGaAs,etc. has a small resistance between the Q-switch region and the gainregion. Accordingly, when the potential difference between the Q-switchregion and the gain region becomes larger, a leakage current between theQ-switch region and the gain region is increased. Such a leakage currentinhibits the Q-switch operation due to various factors. For example, thepassive Q-switch pulse semiconductor laser has a smaller variation inthe Q-value when the leakage current becomes larger than a photocurrentof the Q-switch region. It is necessary for the active Q-switch pulsesemiconductor laser to increase an allowable current of a switchingelement, thus lowering a switching speed.

It is conceivable to form a groove in the separation region as a methodof increasing a resistance between the Q-switch region and the gainregion. The formation of the groove in the separation region causesincrease in guide loss, increase in stimulated emission in the gainregion due to light reflection in the separation region, and lowering ofa pulse energy due to laser oscillation. As a method of increasing aresistance between two electrodes while maintaining optical couplingbetween the two electrodes, it has been proposed to provide, in a regiondistant from a light emission region, a separation groove that reaches asubstrate, and to remove, in a vicinity of the light emission region,only a n-type GaAs electrode layer in a surface layer (JapaneseUnexamined Patent Application Publication No. H1-262683). In such acase, however, a p-type AlGaAs cladding layer exists under the n-typeGaAs electrode layer, thus causing a current leakage to occur via thep-type AlGaAs cladding layer. As another method of increasing aresistance between two electrodes, there has been proposed a method ofperforming ion injection between the two electrodes (Japanese UnexaminedPatent Application Publication No. 2008-258274). In such a case,however, there is a possibility that increase in defect due to the ioninjection may cause increase in the guide loss to lower long-termreliability. Further, in a case where a conductivity type is inversed bythe ion injection, a current path is generated in an inversion regiondue to the defect, etc., thus making it difficult to ignore theinfluence due to the current leakage.

In contrast, in the semiconductor laser 1 according to the presentembodiment, the reverse bias voltage is applied to the Q-switch region20 b. Further, when the reverse bias voltage of the separation region 20c is small and is not sufficient, for example, the depletion region 37is formed at a part, of the active layer 23, corresponding to a lowerpart of the Q-switch region 20 b and at a boundary part, of the firstupper cladding layer 25, between the Q-switch region 20 b and theseparation region 20 c, as illustrated in FIG. 14A. However, when thereverse bias voltage of the separation region 20 c becomes larger, forexample, the depletion region 37 is formed at a part, of the activelayer 23, corresponding to a lower part of the Q-switch region 20 b andat a boundary part, of each of the active layer 23, the upper guidelayer 24, and the first upper cladding layer 25, between the Q-switchregion 20 b and the separation region 20 c, as illustrated in FIG. 14B.In this example, the active layer 23 has a thickness of 200 nm, theupper guide layer 24 has a thickness of 100 nm, and the first uppercladding layer 25 has a thickness of 350 nm. In addition, the activelayer 23, the upper guide layer 24, and the first upper cladding layer25 have an average carrier density of 1×10¹⁷ cm⁻³. In such a case, whenthe reverse bias voltage of −10 V is applied to the Q-switch region 20b, an upper end of the depletion region 37 is located at 375 nm from thep-n junction 20J. Moreover, the active layer 23 has a thickness of 200nm, the upper guide layer 24 has a thickness of 100 nm, and the firstupper cladding layer 25 has a thickness of 350 nm. In addition, theactive layer 23, the upper guide layer 24, and the first upper claddinglayer 25 have an average carrier density of 5×10¹⁶ cm⁻³. In such a case,when the reverse bias voltage of −10 V is applied to the Q-switch region20 b, the upper end of the depletion region 37 is located at 550 nm fromthe p-n junction 20J. In both cases, the upper end of the depletionregion 37 is located above the active layer 23. Accordingly, holesgenerated by optical absorption are immediately discharged from anelectric field applied to the active layer 23, and an amount of opticalabsorption is increased. Further, the depletion region 37 expands up tothe separation region 20 c, and thus a part between the gain region 20 aand the Q-switch region 20 b (i.e., the separation region 20 c) has ahigher resistance of 100 kohms or more. As a result, it becomes possibleto cause a current leakage from the gain region 20 a to the Q-switchregion 20 b to be 1 mA or less, and thus to make the current leakagesmall enough to be almost ignored. Moreover, light scattering ofcarriers in the gain region 20 a is suppressed to increase injectioncarrier density, thus making it possible to allow for higher power ofthe semiconductor laser 1.

2. Modification Examples of First Embodiment

Next, description is given of a modification example of thesemiconductor laser 1 according to the foregoing embodiment.

Modification Example A

In the foregoing embodiment, for example, the voltage V3 outputted fromthe drive circuit (e.g., the laser driver 304 described later) mayinclude a pulse voltage waveform according to the application of thepulse voltage V1, as illustrated in FIG. 21. The voltage V3 may include,for example, a pulse voltage waveform that has a peak in a negativedirection after the pulse voltage V1 is applied to the gain region 20 a(e.g., at a time when the peak of the pulse voltage V1 is passed). Inthe voltage V3, the above-described pulse voltage waveform may include apulse voltage waveform that has a peak in the negative direction in aperiod of time when the pulse voltage V1 is applied to the gain region20 a and when the peak of the pulse voltage V1 is passed. That is, thevoltage V3 may include a pulse voltage waveform that falls and rises inthe period of time when the pulse voltage V1 is applied to the gainregion 20 a.

At this occasion, the drive circuit (e.g., the laser driver 304described later) outputs, for example, the reverse bias (the voltage V2)of negative several volts (voltage V2<0), as indicated by alternate longand short dash lines in FIG. 21. However, the pulse voltage waveformhaving a peak in the negative direction of the voltage V3 causes a pulsevoltage fluctuation having a peak in a positive direction to occur in avoltage V2′ of the Q-switch region 20 b (the Q-switch electrode 32). Thevoltage V2′ may include, for example, a pulse voltage waveform that hasa peak in the positive direction after the pulse voltage V1 is appliedto the gain region 20 a (e.g., at the time when the peak of the pulsevoltage V1 is passed). That is, the voltage V3 has an active waveformoutputted from the drive circuit (e.g., the laser driver 304 describedlater), and the voltage V2 has a passive waveform generated due to thevoltage fluctuation caused by the voltage V3.

In such a case, the depletion region 37 makes transition from a stateillustrated in FIG. 14B to a state illustrated in FIG. 14A; that is, aleakage current is generated between the gain region 20 a and theQ-switch region 20 b. The leakage current causes voltage drop due toresistance of the Q-switch region 20 b; when loss of the Q-switch region20 b is actively lowered, a gain exceeds the loss, thus causing thelaser oscillation to occur. The photocurrent of the Q-switch region 20 bundergoes voltage drop similarly to the passive Q-switch method.Accordingly, an increasing speed of the Q-value is enhanced, thusallowing for obtainment of the pulse light having a high peak value.

Modification Example B

In the foregoing embodiment and the modification example thereof, forexample, the width (the width of the ridge part 20A in thewidth-direction) D3 of the separation region 20 c may be equal to thewidth D1 of the gain region 20 a and to the width D2 of the Q-switchregion 20 b, as illustrated in FIG. 22. In such a case as well, anoptical loss in the separation groove 20B is very small, and thus itbecomes possible to allow for higher power of the semiconductor laser 1.

Modification Example C

In the foregoing embodiment and the modification examples thereof, forexample, the impurity diffusion region 25C may be provided only in theridge part 20A, as illustrated in FIG. 23. In such a case as well, it ispossible to homogenize impurity density in the impurity diffusion region25C.

Modification Example D

In the foregoing embodiment and the modification examples thereof, forexample, a region similar to the impurity diffusion region 25C (animpurity diffusion region 25D) may be provided also in the Q-switchregion 20 b, as illustrated in FIG. 24. In this case, the p-n junction20J is formed at a position lower than the part corresponding to thefoot of each of both the sides of the ridge part 20A, similarly to theforegoing embodiment and the modification examples thereof. Accordingly,the depletion region 37 expands up to the separation region 20 c, andthus the part between the gain region 20 a and the Q-switch region 20 b(i.e., the separation region 20 c) has a higher resistance of 100 kohmsor more. As a result, it becomes possible to cause a current leakagefrom the gain region 20 a to the Q-switch region 20 b to be 1 mA orless, and thus to make the current leakage small enough to be almostignored.

Modification Example E

In the foregoing embodiment and the modification examples thereof, forexample, the etching stop layers 25A and 25B may be omitted, asillustrated in FIGS. 25, 26, and 27.

2. Second Embodiment

Next, description is given of a distance measuring unit 3 according to asecond embodiment of the present disclosure. FIG. 28 illustrates aschematic configuration example of the distance measuring unit 3. Thedistance measuring unit 3 measures a distance to a test object 100 bymeans of a time-of-flight (TOF) method. The distance measuring unit 3includes the semiconductor laser device 2 as a light source. Thedistance measuring unit 3 includes, for example, the semiconductor laserdevice 2, a light-receiving section 301, lenses 302 and 302, the laserdriver 304, an amplifier section 305, a measuring section 306, a controlsection 307, and an operation section 308.

The light-receiving section 301 detects light reflected by the testobject 100. The light-receiving section 301 is configured by aphotodetector, for example. The light-receiving section 301 may beconfigured by an avalanche photo diode (APD), a single-photon avalanchediode (SPAD), a multi-pixel single-photon avalanche diode (MP-SPAD), orthe like. The lens 302 is a lens that collimates light emitted from thesemiconductor laser device 2; the lens 302 is a collimating lens. Thelens 303 is a lens that condenses light reflected by the test object 100and guides the condensed light to the light-receiving section 301; thelens 303 is a condensing lens.

The laser driver 304 is, for example, a driver circuit that drives thesemiconductor laser device 2 (the semiconductor laser 1). The amplifiersection 305 is, for example, an amplifier circuit that amplifies adetection signal outputted from the light-receiving section 301. Themeasuring section 306 is, for example, a circuit that generates a signalcorresponding to a difference between a single inputted from theamplifier section 305 and a reference signal. The measuring section 306is configured by a Time to Digital Converter (TDC), for example. Thereference signal may be either a signal inputted from the controlsection 307 or an output signal of a detection section that directlydetects an output of the semiconductor laser device 2. The controlsection 307 is, for example, a processor that controls thelight-receiving section 301, the laser driver 304, the amplifier section305, and the measuring section 306. The operation section 308 is acircuit that derives distance information on the basis of the signalgenerated by the measuring section 306.

The distance measuring unit 3 may include, for example, a polarizationbeam splitter (PBS) 309 between the lens 302 and the test object 100 aswell as a reflection mirror 310 that causes light reflected by the PBS309 to enter the light-receiving section 301, as illustrated in FIG. 29.In such a case, light emitted from the semiconductor laser device 2 andlight reflected by the test object 100 pass through the same opticalpath between the PBS 309 and the test object 100, thus making itpossible to enhance measuring accuracy.

The distance measuring unit 3 may include, between the lens 302 and thetest object 100, a scanning section 311 that scans the light emittedfrom the semiconductor laser device 2, for example, as illustrated inFIG. 30. For example, the scanning section 311 performs measurement ofdistance information of the test object 100 on a single axis, i.e.,two-dimensional measurement. The distance measuring unit 3 illustratedin FIG. 29 performs distance measurement of only one location of thetest object 100, i.e., one-dimensional measurement of only a rangedirection. In contrast, the distance measuring unit 3 illustrated inFIG. 30 includes the scanning section 311, thus making it possible toperform the two-dimensional measurement.

For example, the scanning section 311 may perform measurement ofdistance information of the test object 100 on two axes, i.e.,three-dimensional measurement. In such a case, it is possible for thedistance measuring unit 3 illustrated in FIG. 30 to perform thethree-dimensional measurement.

The distance measuring unit 3 may include, for example, the PBS 309, thereflection mirror 310, and the scanning section 311, as illustrated inFIG. 31. In such a case, it is possible not only to enhance measuringaccuracy but also to perform the two-dimensional measurement or thethree-dimensional measurement.

In the present embodiment, the semiconductor laser device 2 is used as alight source in the distance measuring unit 3. This makes it possible toemit high-power laser light and thus to enhance detection accuracy.

In the present embodiment, the semiconductor laser device 2 is used as alight source in the distance measuring unit 3. This makes it possible toemit high-power laser light and thus to enhance detection accuracy.

Although the present disclosure has been described hereinabove withreference to a plurality of embodiments and modification examplesthereof, the present disclosure is not limited to the foregoingrespective embodiments, and may be modified in a variety of ways. It isto be noted that the effects described herein are merely examples. Theeffects of the present disclosure are not limited to those describedherein. The present disclosure may have effects other than thosedescribed herein.

Moreover, for example, the present disclosure may have the followingconfigurations.

(1)

A semiconductor laser including, on a semiconductor substrate:

a first semiconductor layer of a first conductivity type;

an active layer;

a second semiconductor layer of a second conductivity type, in order;

a ridge part formed in the second semiconductor layer and extending in astacked in-plane direction; and

an electrode,

the ridge part having a structure in which a plurality of gain regionsand a plurality of Q-switch regions are each disposed alternately witheach of separation regions being interposed therebetween in an extendingdirection of the ridge part,

the separation regions each having a separation groove that separatesfrom each other, by a space, the gain region and the Q-switch regionadjacent to each other,

the separation groove having a bottom surface at a position, in thesecond semiconductor layer, higher than a part corresponding to a footof each of both sides of the ridge part,

the electrode being provided over the bottom surface with an insulatinglayer being interposed therebetween.

(2)

The semiconductor laser according to (1), in which

the second semiconductor layer includes a firstdifferent-composition-ratio semiconductor layer having a compositionratio different from a composition ratio of another part of the secondsemiconductor layer, and

the bottom surface is a portion of a top surface of the firstdifferent-composition-ratio semiconductor layer.

(3)

The semiconductor laser according to (2), in which

the second semiconductor layer includes a seconddifferent-composition-ratio semiconductor layer having a compositionratio different from the composition ratio of the other part of thesecond semiconductor layer, and

a top surface of the part corresponding to the foot of each of both thesides of the ridge part is a portion of a top surface of the seconddifferent-composition-ratio semiconductor layer.

(4)

The semiconductor laser according to any one of (1) to (3), in whicheach of the bottom surface and the top surface of the part correspondingto the foot of each of both the sides of the ridge part is a surfaceformed by wet etching.

(5)

The semiconductor laser according to any one of (1) to (4), in which thesemiconductor laser includes a p-n junction at a position lower than thepart corresponding to the foot of each of both the sides of the ridgepart.

(6)

The semiconductor laser according to any one of (1) to (5), in which thesecond semiconductor layer includes, at a part corresponding to each ofthe gain regions, an impurity diffusion region of the secondconductivity type having an impurity concentration relatively higherthan an impurity concentration of a part corresponding to each of theQ-switch regions.

(7)

An electronic apparatus including a semiconductor laser as a lightsource,

the semiconductor laser including, on a semiconductor substrate,

a first semiconductor layer of a first conductivity type,

an active layer,

a second semiconductor layer of a second conductivity type, in order,

a ridge part formed in the second semiconductor layer and extending in astacked in-plane direction, and

an electrode,

the ridge part having a structure in which a plurality of gain regionsand a plurality of Q-switch regions are each disposed alternately witheach of separation regions being interposed therebetween in an extendingdirection of the ridge part,

the separation regions each having a separation groove that separatesfrom each other, by a space, the gain region and the Q-switch regionadjacent to each other,

the separation groove having a bottom surface at a position, in thesecond semiconductor layer, higher than a part corresponding to a footof each of both sides of the ridge part,

the electrode being provided over the bottom surface with an insulatinglayer being interposed therebetween.

(8)

The electronic apparatus according to (7), further including a drivesection that drives the semiconductor laser,

the drive section applying a forward bias pulse voltage to the gainregion,

the drive section applying a reverse bias to the Q-switch region, and

the drive section applying a forward bias to the electrode.

(9)

The electronic apparatus according to (7), in which a forward bias to beapplied to the electrode has a pulse voltage waveform having a peak in anegative direction in a period of time when the pulse voltage is appliedto the gain region and when a peak of a waveform of the pulse voltage tobe applied to the gain region is passed.

(10)

A method of driving a semiconductor laser,

the semiconductor laser including, on a semiconductor substrate,

a first semiconductor layer of a first conductivity type,

an active layer,

a second semiconductor layer of a second conductivity type, in order,

a ridge part formed in the second semiconductor layer and extending in astacked in-plane direction, and

an electrode,

the ridge part having a structure in which a plurality of gain regionsand a plurality of Q-switch regions are each disposed alternately witheach of separation regions being interposed therebetween in an extendingdirection of the ridge part,

the separation regions each having a separation groove that separatesfrom each other, by a space, the gain region and the Q-switch regionadjacent to each other,

the separation groove having a bottom surface at a position, in thesecond semiconductor layer, higher than a part corresponding to a footof each of both sides of the ridge part,

the electrode being provided over the bottom surface with an insulatinglayer being interposed therebetween,

the method including:

applying a forward bias pulse voltage to the gain region;

applying a reverse bias to the Q-switch region; and

applying a forward bias to the electrode.

(11)

The method of driving the semiconductor laser according to (10), inwhich the pulse voltage has a pulse width of a nano-second order.

(12)

The method of driving the semiconductor laser according to (11), inwhich the forward bias includes a direct current.

This application claims the benefit of Japanese Priority PatentApplication JP2016-162773 filed with the Japan Patent Office on Aug. 23,2016, the entire contents of which are incorporated herein by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations, and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A semiconductor laser comprising, on a semiconductor substrate: afirst semiconductor layer of a first conductivity type; an active layer;a second semiconductor layer of a second conductivity type, in order; aridge part formed in the second semiconductor layer and extending in astacked in-plane direction; and an electrode, the ridge part having astructure in which a plurality of gain regions and a plurality ofQ-switch regions are each disposed alternately with each of separationregions being interposed therebetween in an extending direction of theridge part, the separation regions each having a separation groove thatseparates from each other, by a space, the gain region and the Q-switchregion adjacent to each other, the separation groove having a bottomsurface at a position, in the second semiconductor layer, higher than apart corresponding to a foot of each of both sides of the ridge part,the electrode being provided over the bottom surface with an insulatinglayer being interposed therebetween.
 2. The semiconductor laseraccording to claim 1, wherein the second semiconductor layer includes afirst different-composition-ratio semiconductor layer having acomposition ratio different from a composition ratio of another part ofthe second semiconductor layer, and the bottom surface is a portion of atop surface of the first different-composition-ratio semiconductorlayer.
 3. The semiconductor laser according to claim 2, wherein thesecond semiconductor layer includes a second different-composition-ratiosemiconductor layer having a composition ratio different from thecomposition ratio of the other part of the second semiconductor layer,and a top surface of the part corresponding to the foot of each of boththe sides of the ridge part is a portion of a top surface of the seconddifferent-composition-ratio semiconductor layer.
 4. The semiconductorlaser according to claim 3, wherein each of the bottom surface and thetop surface of the part corresponding to the foot of each of both thesides of the ridge part is a surface formed by wet etching.
 5. Thesemiconductor laser according to claim 1, wherein the semiconductorlaser comprises a p-n junction at a position lower than the partcorresponding to the foot of each of both the sides of the ridge part.6. The semiconductor laser according to claim 1, wherein the secondsemiconductor layer includes, at a part corresponding to each of thegain regions, an impurity diffusion region of the second conductivitytype having an impurity concentration relatively higher than an impurityconcentration of a part corresponding to each of the Q-switch regions.7. An electronic apparatus comprising a semiconductor laser as a lightsource, the semiconductor laser including, on a semiconductor substrate,a first semiconductor layer of a first conductivity type, an activelayer, a second semiconductor layer of a second conductivity type, inorder, a ridge part formed in the second semiconductor layer andextending in a stacked in-plane direction, and an electrode, the ridgepart having a structure in which a plurality of gain regions and aplurality of Q-switch regions are each disposed alternately with each ofseparation regions being interposed therebetween in an extendingdirection of the ridge part, the separation regions each having aseparation groove that separates from each other, by a space, the gainregion and the Q-switch region adjacent to each other, the separationgroove having a bottom surface at a position, in the secondsemiconductor layer, higher than a part corresponding to a foot of eachof both sides of the ridge part, the electrode being provided over thebottom surface with an insulating layer being interposed therebetween.8. The electronic apparatus according to claim 7, further comprising adrive section that drives the semiconductor laser, the drive sectionapplying a forward bias pulse voltage to the gain region, the drivesection applying a reverse bias to the Q-switch region, and the drivesection applying a forward bias to the electrode.
 9. The electronicapparatus according to claim 7, wherein a forward bias to be applied tothe electrode has a pulse voltage waveform having a peak in a negativedirection in a period of time when the pulse voltage is applied to thegain region and when a peak of a waveform of the pulse voltage to beapplied to the gain region is passed.
 10. A method of driving asemiconductor laser, the semiconductor laser including, on asemiconductor substrate, a first semiconductor layer of a firstconductivity type, an active layer, a second semiconductor layer of asecond conductivity type, in order, a ridge part formed in the secondsemiconductor layer and extending in a stacked in-plane direction, andan electrode, the ridge part having a structure in which a plurality ofgain regions and a plurality of Q-switch regions are each disposedalternately with each of separation regions being interposedtherebetween in an extending direction of the ridge part, the separationregions each having a separation groove that separates from each other,by a space, the gain region and the Q-switch region adjacent to eachother, the separation groove having a bottom surface at a position, inthe second semiconductor layer, higher than a part corresponding to afoot of each of both sides of the ridge part, the electrode beingprovided over the bottom surface with an insulating layer beinginterposed therebetween, the method comprising: applying a forward biaspulse voltage to the gain region; applying a reverse bias to theQ-switch region; and applying a forward bias to the electrode.
 11. Themethod of driving the semiconductor laser according to claim 10, whereinthe pulse voltage has a pulse width of a nano-second order.
 12. Themethod of driving the semiconductor laser according to claim 11, whereinthe forward bias comprises a direct current.